The present invention relates to a fuel cell arrangement as well as to a method for controlling the humidity of a reactant for a fuel cell arrangement.
Fuel cells, in particular fuel cells driven with pure hydrogen, are considered today to be the powertrain of the future due to the fact that they emit only pure water. Such fuel cells have, in particular, a fuel cell membrane which also requires water in the form of steam. The steam is used thereby to ensure a sufficiently high ionic conductivity within the fuel cell through the membrane.
In the case of known fuel cell arrangements, this steam can be fed into the fuel cells that comprise at least one of the two reactants, which react with one another in the fuel cell. In order to assure an optimal operation of the fuel cell arrangement, it is necessary to monitor and in particular to control or adjust this humidity. An open-loop or closed-loop control arrangement is thus known, for example, from the German patent publication DE 10 2008 020 102 A1 for the open-loop control or closed-loop control of the water volume of at least one of the reactants supplied to the fuel cells. Provision is thereby made for a dew point measurement sensor and a temperature sensor, which are used to determine the humidity of the at least one reactant. A dew point measurement sensor can be designed in a known manner as a semiconductor sensor and is thus, like other humidity sensors, susceptible to interference if drops form in the reactant. An accumulation of liquid water can particularly lead to errant measurements.
The WIPO patent publication WO 2008/034253 likewise discloses a control system for the humidity of a reactant in a fuel cell arrangement. In this case, a pressure and a temperature sensor are used in order to determine the humidity of the reactant by means of a complicated calculation. It is furthermore necessary for this calculation to include the mass flow of the reactant and the mass flow of water supplied by a humidifying device in the calculation. In so doing, this calculation is also susceptible to faults due to the plurality of input parameters, in particular if only one of the sensors breaks down or malfunctions.